In recent years, with rapid spread of demand for wireless communication, various wireless communication standards using different wireless communication schemes have been used and co-existed. Among them, a wireless communication apparatus having a so-called multimode function for supporting a plurality of different wireless communication schemes and providing users with a seamless connection environment has been strongly demanded.
For example, for an example of a method for implementing multimode functions in wireless communication apparatus, as disclosed in Patent Document 1 and Patent Document 2, a method for enabling switching of wireless communication functions in wireless communication apparatus by changing software programs, configuration parameters, etc, has been proposed. This configuration is called a software defined radio or a reconfigurable wireless apparatus.
Next, as an example, the configuration and operation of the conventional software defined radio that changes its function to supporting a plurality of wireless communication systems will be described with reference to FIG. 1. To be more specific, the switching of the function of the software defined radio between a wireless communication scheme supporting a WCDMA (wideband CDMA) mobile telephone system standard, which is one of the third-generation mobile telephone system standard (hereinafter referred to as the “WCDMA scheme”) and a wireless communication scheme supporting an IEEE802.11a standard, which is one of the wireless LAN systems (hereinafter “the IEEE802.11a scheme”) will be described below.
In FIG. 1, wireless communication apparatus 10 can change its wireless communication process function, and includes analog signal processing section 15, analog-to-digital converting section 20, reconfigurable digital signal processing section 30, bus 60, reconfiguration control bus 65, communication control section 70, timer 75, reconfiguration memory 80, and reconfiguration control section 85. Analog signal processing section 15, analog-to-digital converting section 20, and reconfigurable digital signal processing section 30 are configured to change process functions by changing software programs or configuration parameters.
Reconfigurable digital signal processing section 30 includes reconfigurable signal processing module 40, I/O sections 35 and 50, and a general-purpose memory 55. Reconfigurable signal processing module 40 performs a series of digital wireless communication processes supporting the WCDMA scheme and the IEEE802.11a scheme, such as codec processes, modem processes, a multiplexing process, a synchronization process, and a filtering process. Reconfiguration control section 85 changes the process functions of the reconfigurable signal processing module by reading predetermined configuration software programs or configuration parameters stored in reconfiguration memory 80 and supplying the read information to the reconfigurable signal processing module through reconfiguration control bus 65.
For example, when the function of wireless communication apparatus 10 is changed to support the WCDMA scheme, reconfigurable digital signal processing section 30 is set to process codec processes, such as convolutional coding, turbo coding, and decoding supporting the coding, modem processes, such as a modem process supporting the QPSK modulation scheme, multiplexing processes, such as code division multiplexing using a direct sequence spread spectrum and a demultiplexing process corresponding thereto, a synchronization process, such as a process of synchronizing a scramble code or a synchronizing channel supporting the WCDMA standard, and a filtering process, such as a transmission and reception filtering process satisfying root Nyquist characteristics.
When wireless communication is performed between wireless communication apparatus 10 and another wireless communication apparatus, such as a base station of the WCDMA mobile telephone system, analog signal processing section 15 performs analog processes such as amplification with predetermined gain, frequency conversion and frequency selection, on digitally modulated signals received through an antenna, and analog-to-digital converting section 20 quantizes the analog processed signals to generate a digital data sequence and outputs the digital data sequence to reconfigurable digital signal processing section 30. In reconfigurable digital signal processing section 30, the digital data sequence is inputted to reconfigurable signal processing module 40 through I/O section 35, and reconfigurable signal processing module 40 performs predetermined demodulation and decoding processing supporting the WCDMA scheme on the received digital data sequence. The bit data sequence finally obtained is temporarily stored in general-purpose memory 55 through I/O section 50, and then read from the memory through bus 60 in order for processing in subsequent upper-layer such as the application layer.
When wireless communication apparatus 10 performs a receiving process, a WCDMA downlink signal is synchronized, and only data required for a subsequent receiving process is selected at the synchronization timing and then outputted to the next processing system. In addition, timing information related to the WCDMA scheme is supplied to timer 75. Timer 75 starts the timer operation in synchronization with the system timing, based on this system timing information. To be more specific, timer 75 includes a counter that performs a counting operation in synchronization with the frame timing of the system.
In contrast, when wireless communication apparatus 10 needs to transmit uplink signals to the base station and a transmission bit data sequence is temporarily accumulated in memory 55 through bus 60, communication control section 70 determines the start timing of the uplink transmission process based on the system timing information from timer 75, and transmits transmission start timing information to timer 75.
To be more specific, this is equivalent to writing the counter value which shows the transmission start timing. If the count value matches with the transmission start timing, timer 75 transmits a transmission process start enable signal, to I/O section 50. When receiving the transmission process start enable signal, I/O section 50 sequentially reads the transmission bit data sequence that is temporarily stored in general-purpose memory 55, and supplies the read data to reconfigurable signal processing module 40. Reconfigurable signal processing module 40 performs predetermined transmission signal processing supporting the uplink transmission process of the WCDMA scheme. The obtained transmission digital modulated signal is transmitted to analog-to-digital converting section 20 through I/O section 35, and then converted into an analog signal by analog-to-digital converting section 20. Then, analog signal processing section 15 performs predetermined analog processes, such as predetermined band limiting, frequency conversion, and amplification on the analog signal, and the processed analog signal is by wireless transmitted to the base station through the antenna.
When the communication process function of wireless communication apparatus 10 is switched from the WCDMA scheme to the IEEE802.11a scheme, wireless communication apparatus 10 operates as follows. That is, reconfiguration control section 85 reads, from reconfiguration memory 80, software programs or configuration parameters for setting the process function of reconfigurable signal processing module 40 to a predetermined function supporting theIEEE802.11a scheme, and supplies the read data to reconfigurable signal processing module 40 through reconfiguration control bus 65. In this way, the function of the signal processing module is changed.
For example, as the codec processes, convolutional coding and Viterbi decoding corresponding thereto are set. As the primary modem processes, any one of BPSK, QPSK, 16QAM, and 64QAM and a modulating and demodulating process corresponding thereto are set. As the multiplexing process, an OFDM (orthogonal frequency division multiplexing) process is set. As the synchronization process, a synchronization process using a short training symbol or a long training symbol supporting the IEEE802.11a scheme is set. As the filtering process, a transmission filtering process satisfying the transmission spectrum requirement of the IEEE802.11a scheme, or a reception filtering process for canceling noise is set.
When wireless communication is performed between wireless communication apparatus 10 and another wireless communication apparatus, such as a wireless LAN station, according to the IEEE802.11a scheme, analog signal processing section 15 performs analog processes, such as predetermined amplification, frequency conversion, and frequency selection, on an OFDM digital modulated signal that is received through the antenna, and analog-to-digital converting section 20 quantizes the result into a digital signal, and outputs the resulting digital data sequence to reconfigurable digital signal processing section 30. In reconfigurable digital signal processing section 30, the digital data sequence is inputted to reconfigurable signal processing module 40 through I/O section 35, and reconfigurable signal processing module 40 performs predetermined demodulating and decoding process supporting the IEEE802.11a scheme on the received digital data sequence. The received bit data sequence finally obtained is temporarily stored in general-purpose memory 55 through I/O section 50, and then read from the memory through bus 60 to be used in processing in subsequent upper-layers such as the application layer. When wireless communication apparatus 10 performs this receiving process, wireless communication apparatus 10 performs a synchronization process on signals received from the communicating station according to the IEEE802.11a scheme, to obtain information about the timing, and the information about the timing is provided to timer 75.
When wireless communication apparatus 10 transmits an ACK signal or data to the communicating station, communication control section 70 determines transmission timing based on the timing information set in timer 75 and a predetermined regulation of a MAC layer, and transmission signal processing supporting the IEEE802.11a scheme is performed based on the same control operation as in the transmission process supporting the WCDMA scheme.
In this way, wireless communication apparatus 10 performs a wireless communication processes supporting one of the WCDMA scheme and the IEEE802.11a scheme. In this case, in reconfigurable digital signal processing section 30, when signal processing related to the transmission and reception of signals is performed, the processing delay time between the input timing of transmission bit data and the output timing of a transmission digital modulated signal from the final stage occurs due to, for example, buffering delay caused by a latch process, a pipeline process or serial/parallel conversion. In addition, in analog signal processing section 15 or analog-to-digital converting section 20, when the function thereof is changed to support the wireless communication scheme of the WCDMA scheme or the IEEE802.11a scheme, analog signal processing characteristics are changed, or a processing system is switched, and, with this, the delay time between the input and the output is likely to change.
Therefore, in order for wireless communication apparatus 10 to perform wireless transmission at the transmission timing that is prescribed by the wireless communication standard, as described above, it is necessary to correct the process start timing taking into account the processing delay time occurring in each of reconfigurable digital signal processing section 30, analog signal processing section 15, and analog-to-digital converting section 20.
To be more specific, it is necessary to advance the start timing of transmission signal processing in reconfigurable digital signal processing section 30 by a time corresponding to the processing delay time. In order to advance the transmission timing, the following method can be used: a processing delay time occurring in each processing section can be estimated in advance in the shipping stage, and the estimated processing delay time is stored semi-fixedly in communication control section 70; and when determining the actual start timing of a transmission process, wireless communication apparatus 10 sets the value of timer 75 such that a transmission process enable signal is outputted at the timing the processing delay time earlier than the original transmission timing.
When wireless communication apparatus 10 changes its wireless communication function, the processing delay time occurring in each processing section is likely to change. Therefore, the processing delay time may vary between supporting wireless communication schemes. In this case, it is possible to perform wireless communication satisfying the requirement with respect to wireless transmission timing by estimating and storing the amount of processing delay occurring in each processing section when the function thereof is set to supporting wireless communication schemes in the shipping stage, reading the amount of processing delay corresponding to the current wireless communication function every time transmission control is performed, and correcting the transmission timing corresponding to the delay amount.
In addition to the timing correction during the transmission process, other communication control factors may need to be corrected when the function of wireless communication apparatus 10 is changed. For example, system synchronization timing may need to be corrected based on a processing delay time when the wireless communication apparatus performs a receiving process. In addition, when received power is measured, the measured value may need to be corrected according to the difference between gains set in the processing sections.    Patent Document 1: Japanese Patent No. 3348196    Patent Document 2: Japanese Patent Application Laid-Open No. 2002-335186